The present invention relates generally to a method for manufacturing a resistance RAM device, and more particularly, to a method for manufacturing a resistance RAM device, which can secure switching characteristics.
Memory devices can generally be classified as volatile random access memory (RAM), which requires power to maintain stored information, or nonvolatile read only memory (ROM), which can retain the stored state of inputted information even when power is interrupted. Examples of volatile RAM include dynamic RAM (DRAM) and an static (SRAM), and an example of nonvolatile ROM is a flash memory device such as electrically erasable and programmable ROM (EEPROM).
Typical DRAM devices are generally considered excellent memory devices; however, DRAM must have high charge storing capacity. In order to obtain a high charge storing capacity, the surface area of an electrode must be increased, thereby making it difficult to accomplish a high level of integration. Further, in a flash memory device two gates are stacked on each other. As a consequence, a high operation voltage is required relative to the power supply voltage; and therefore, a separate booster circuit is necessary for generating the voltage required for write and delete operations. This also in turn makes it difficult to accomplish a high level of integration.
With these constraints in mind, memory devices under development have faced demands for a simple configuration capable of accomplishing a high level of integration while retaining the desirable characteristics of non-volatile memory devices. Currently, memory devices considered as having potential as next-generation memory devices include phase change RAM, resistance RAM (hereinafter referred to as an “ReRAM”), and magnetic RAM.
Among these memory devices, the ReRAM device is a memory device realized by placing a binary transition metal oxide (hereinafter referred to as a “TMO”), capable of storing information according to two resistant states, between a bottom electrode and a top electrode. As an optional electric signal is applied to the TMO, the ReRAM device can store information by taking advantage of the characteristics of the TMO, in which the TMO can be changed from an off state where the TMO has high resistance to be “non-conductive” to an on state where the TMO has low resistance to be “conductive” and the reverse.
Such ReRAM device provides advantages in that an ReRAM exhibits the characteristics of a nonvolatile memory device, has a simple structure, and can be easily manufactured when compared to a typical RAM device and a flash memory device, since the ReRAM is configured by interposing the TMO between the bottom electrode and the top electrode.
However in conventional ReRAM devices, an ideal etching profile is not obtained in an etching process for forming patterns, and the sides of the top electrode tend to be etched to a great extent. This in turn causes a problem in that the switching characteristics of the ReRAM device are likely to deteriorate.
In detail, the on and off characteristics of the ReRAM are determined according to a filament path which is produced on the interface of the TMO. In this regard, if the area of the interface between the top electrode and the TMO decreases, the filament path in the on state is most likely reduced, whereby a switching margin decreases.
Accordingly, if the ideal etching profile is not obtained, and the sides of the top electrode are etched to a great extent when conducting etching for forming the top electrode and the TMO; the area of the interface between the top electrode and the TMO cannot but decrease. In particular, when the size of an ReRAM device is decreased, the areas of the TMO and the top electrode are decreased in comparison to the area of the bottom electrode; and therefore the conventional ReRAM device has a drawback in that switching characteristics cannot be secured.